Our objective is to investigate how the characteristics of the central nervous regulation of body temperature change as a function of electrophysiologically defined arousal states and circadian time. We also are describing the influences of peripheral and central temperatures on the normative distribution of arousal states. Comparative thermoregulatory and electrophysiological studies are being made of sleep, shallow torpor, and hibernation. Lastly, we are seeking neurophysiological correlates of the above phenomena by making extracellular recordings from temperature-sensitive hypothalamic units in unanesthetized, unrestrained animals during wakefulness, sleep, and torpor.